In the process of shipping an item from one location to another, a protective packaging material is typically placed in the shipping case, or box, to fill any voids and/or to cushion the item during the shipping process. Plastic foam peanuts and plastic bubble pack are two types of conventionally used packaging materials and these plastic materials, while performing acceptably in many packaging applications, are not without disadvantages. For example, one drawback of plastic bubble film is that it usually includes a polyvinylidene chloride coating which prevents the plastic film from being safely incinerated thereby creating disposal difficulties for some industries. Additionally, both the plastic foam peanuts and the plastic bubble pack have a tendency to generate a charge of static electricity which attracts dust from the surrounding packaging site. Furthermore, these plastic materials sometimes themselves produce a significant amount of packaging "lint." Such dust and lint particles are generally undesirable and may even be destructive to sensitive merchandise such as electronic or medical equipment.
However, perhaps the most serious drawback of plastic bubble wrap and/or plastic foam peanuts is their effect on our environment. Quite simply, these plastic packaging materials are not biodegradable and thus they cannot avoid further multiplying our planet's already critical waste disposal problems. The non-biodegradability of these packaging materials has become increasingly important in light of many industries adopting more progressive policies in terms of environmental responsibility.
These and other disadvantages of conventional plastic packaging materials have made paper protective packaging material a very popular alternative. Paper is biodegradable, recyclable and renewable thereby making it an environmentally responsible choice for conscientious industries. Additionally, paper may be safely incinerated by the recipients of the products. Furthermore, paper protective packaging material is perfect for particle-sensitive merchandise, as its clean dust-free surface is resistant to static cling.
While paper in a sheet-like form could possibly be used as a protective packaging material, it is usually preferable to convert sheet-like stock material into a relatively low density pad-like cushioning product. This conversion may be accomplished by a cushioning conversion machine, such as those disclosed in U.S. Pat. Nos. 3,509,798; 3,603,216; 3,655,500; 3,779,039; 4,026,198; 4,109,040; 4,717,613; and 4,750,896, and co-pending U.S. patent application Ser. Nos. 07/592,572 and 07/712,203. The entire disclosures of these patents and applications, which are owned by the assignee of the present application, are hereby incorporated by reference.
In a typical cushioning conversion machine, a sheet-like stock material will form the starting material for the conversion process and this stock material will usually be composed of one or more layers of paper. Each of these layers, and thus the stock material itself, may be viewed as having two lateral edge sections and a central section therebetween. The cushioning conversion machine will generally include a conversion assembly for converting the sheet-like stock material into a cushioning product and a supply assembly which supplies the sheet-like stock material to the conversion assembly. The design of most stock supply assemblies results in the stock material being supplied to the conversion assembly in such a manner that its lateral edge sections must travel in a longer path than its central section whereby tension is created in the edge sections. If this "edge-tension" reaches a certain magnitude, a continuous tear is formed in one or more layers of the stock material which, understandably, inhibits the ability of the conversion assembly to create an acceptable cushioning product.
Applicants attempted to eliminate this "continuous tear" problem by artificially increasing the "central" path between the stock supply assembly and the conversion assembly whereby any tension would be shifted from the edge sections to the central section. This approach was based on the theory that if the central section of the stock material had to travel the same distance as the edge sections, the edge-tension, and therefore the continuous tearing, would be eliminated. Applicants postulated correctly in one regard as this solution did indeed eliminate edge tension and continuous tearing in the stock material. However, the quality of the cushioning product subsequently created from this "edge-tension free" stock material was unsatisfactory. The unacceptable nature of this "edge-tension free" cushioning product is believed to be due to the fact that a certain amount of edge-tension is essential to the proper conversion of the stock material into the cushioning product. In other words, a minimum "conversion-tension" is necessary in the edge sections of the stock material to properly convert the stock material into a cushioning product.
According to the present invention, the "continuous-tear" problem is solved by controlling, rather than eliminating, the tension in the edge sections of the stock material. Specifically, the edge-tension is controlled so that it is greater than or equal to the minimum conversion-tension and less than the continuous tearing-tension. In this manner, continuous tears are eliminated without sacrificing the quality of the created cushioning product.
More particularly, the present invention provides a cushioning conversion machine for converting a sheet-like stock material, which may be viewed as having two edge sections and a central section therebetween, into a cushioning product. The machine includes a conversion assembly for converting the sheet-like stock material into a cushioning product and a supply assembly which supplies the sheet-like stock material to the conversion assembly. The stock material is supplied to the conversion assembly in such a manner that its edge sections must travel in a longer path than the central section thereby creating tension in the edge sections. While a certain minimum conversion-tension is necessary in the lateral edge sections of the stock material to properly convert the stock material into a cushioning product, a certain continuous tearing-tension, greater than the minimum conversion-tension, will cause a continuous tear in the stock material. To insure that the edge-tension is not so great as to cause continuous tearing but is great enough to allow proper conversion, the supply assembly includes an edge-tension controlling device which controls the edge-tension so that it is greater than or equal to the minimum conversion-tension and less than the continuous tearing-tension.
In the preferred embodiment, the edge-tension controlling device controls the edge-tension by creating openings in the stock material. More particularly, the edge-tension controlling device controls edge-tension by creating a series of unconnected tension-relieving tears between the ends sections and the central section of the sheet-like stock material. The device preferably includes a mounting shaft, a pair of edge rollers mounted on opposite ends of the shaft, and a central roller mounted on the shaft between the edge rollers. The rollers are dimensioned and arranged so that a sagging gap is created on each side of the central roller between it and the respective edge roller. In the tension-controlled conversion process, the stock material passes over the rollers whereby the edge rollers are positioned beneath the edge sections and the central roller and the sagging gaps are positioned adjacent the central section. The summation of the width of the edge rollers, the central roller, and the sagging gaps, approximately equals the width of the sheetlike material which in a typical embodiment would be thirty inches.
The edge-tension controlling device is designed so that when the stock material approaches the "continuous-tearing tension", a small tension-relieving tear will begin to form between the edge section and the central section. As the tension-relieving tear opens, the portion of the stock material adjacent the inner border of the tension-relieving tear sags off the respective edge roller into the adjacent sagging gap. In this manner, excessive tension is shifted to the central section of the stock material whereby any additional tearing is eliminated. One may appreciate that during a typical conversion process, the edge-tension controlling device will create a series of unconnected tension-relieving tears between the edge sections and the central section of the stock material.
The present invention provides these and other features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail a certain illustrative embodiment of the invention. However, this embodiment is indicative of but one of the various ways in which the principles of the invention may be employed.